~Cambridge Natural Science Manuals.~
=BIOLOGICAL SERIES.=
GENERAL EDITOR:—ARTHUR E. SHIPLEY, M.A. FELLOW AND TUTOR OF CHRIST’S COLLEGE, CAMBRIDGE.
FOSSIL PLANTS.
~London~: C. J. CLAY AND SONS,
CAMBRIDGE UNIVERSITY PRESS WAREHOUSE,
AVE MARIA LANE,
AND
H. K. LEWIS,
136, GOWER STREET, W.C.
~Glasgow~: 263, ARGYLE STREET.
~Leipzig~: F. A. BROCKHAUS.
~New York~: THE MACMILLAN COMPANY.
~Bombay~: E. SEYMOUR HALE.
TREE STUMPS IN A CARBONIFEROUS FOREST. VICTORIA PARK, GLASGOW.
FOSSIL PLANTS
FOR STUDENTS OF BOTANY AND GEOLOGY
BY
A. C. SEWARD, M.A., F.G.S.
ST JOHN’S COLLEGE, CAMBRIDGE,
LECTURER IN BOTANY IN THE UNIVERSITY OF CAMBRIDGE.
WITH ILLUSTRATIONS.
VOL. I.
CAMBRIDGE:
AT THE UNIVERSITY PRESS.
1898
[All Rights reserved.]
~Cambridge~:
PRINTED BY J. AND C. F. CLAY,
AT THE UNIVERSITY PRESS.
PREFACE.
In acceding to Mr Shipley’s request to write a book on Fossil Plants for the Cambridge Natural History Series, I am well aware that I have undertaken a work which was considered too serious a task by one who has been called a “founder of modern Palaeobotany.” I owe more than I am able to express to the friendship and guidance of the late Professor Williamson; and that I have attempted a work to which he consistently refused to commit himself, requires a word of explanation. My excuse must be that I have endeavoured to write a book which may render more accessible to students some of the important facts of Palaeobotany, and suggest lines of investigation in a subject which Williamson had so thoroughly at heart.
The subject of Palaeobotany does not readily lend itself to adequate treatment in a work intended for both geological and botanical students. The Botanist and Geologist are not always acquainted with each other’s subject in a sufficient degree to appreciate the significance of Palaeobotany in its several points of contact with Geology and recent Botany. I have endeavoured to bear in mind the possibility that the following pages may be read by both non-geological and non-botanical students. It needs but a slight acquaintance with Geology for a Botanist to estimate the value of the most important applications of Palaeobotany; on the other hand, the bearing of fossil plants on the problems of phylogeny and descent cannot be adequately understood without a fairly intimate knowledge of recent Botany.
The student of elementary geology is not as a rule required to concern himself with vegetable palaeontology, beyond a general acquaintance with such facts as are to be found in geological text-books. The advanced student will necessarily find in these pages much with which he is already familiar; but this is to some extent unavoidable in a book which is written with the dual object of appealing to Botanists and Geologists. While considering those who may wish to extend their botanical or geological knowledge by an acquaintance with Palaeobotany, my aim has been to keep in view the requirements of the student who may be induced to approach the subject from the standpoint of an original investigator. As a possible assistance to those undertaking research in this promising field of work, I have given more references than may seem appropriate to an introductory treatise, and there are certain questions dealt with in greater detail than an elementary treatment of the subject requires. In several instances references are given in the text or in footnotes to specimens of Coal-Measure plants in the Williamson cabinet of microscopic sections. Now that this invaluable collection of slides has been acquired by the Trustees of the British Museum, the student of Palaeobotany has the opportunity of investigating for himself the histology of Palaeozoic plants.
My plan has been to deal in some detail with certain selected types, and to refer briefly to such others as should be studied by anyone desirous of pursuing the subject more thoroughly, rather than to cover a wide range or to attempt to make the list of types complete. Of late years there has been a much wider interest evinced by Botanists in the study of fossil plants, and this is in great measure due to the valuable and able work of Graf zu Solms-Laubach. His Einleitung in die Palaeophytologie must long remain a constant book of reference for those engaged in palaeobotanical work. While referring to authors who have advanced the study of petrified plants of the Coal period, one should not forget the valuable services that have been rendered by such men as Butterworth, Binns, Wilde, Earnshaw, Spencer, Nield, Lomax and Hemingway, by whose skill the specimens described by Williamson and others were first obtained and prepared for microscopical examination.
I am indebted to many friends, both British and Continental, for help of various kinds. I would in the first place express my thanks to Professor T. McKenny Hughes for having originally persuaded me to begin the study of recent and fossil plants. I am indebted to Prof. Nathorst of Stockholm, Dr Hartz of Copenhagen, Prof. Zeiller, Dr Renault and Prof. Munier-Chalmas of Paris, Prof. Bertrand of Lille, Prof. Stenzel and the late Prof. Roemer of Breslau, Dr Sterzel of Chemnitz, the late Prof. Weiss of Berlin, the late Dr Stur of Vienna, and other continental workers, as well as to Mr Knowlton of Washington, for facilities afforded me in the examination of fossil plant collections. My thanks are due to the members of the Geological and Botanical departments of the British Museum; also to Mr E. T. Newton of the Geological Survey, and to those in charge of various provincial museums, for their never-failing kindness in offering me every assistance in the investigation of fossil plants under their charge. Prof. Marshall Ward has given me the benefit of his criticism on the section dealing with Fungi; and my friend Mr Alfred Harker has rendered me a similar service as regards the chapter on Geological History. I am especially grateful to my colleague, Mr Francis Darwin, for having read through the whole of the proofs of this volume. To Mr Shipley, as Editor, I am under a debt of obligation for suggestions and help in various forms. I would also express my sense of the unfailing courtesy and skill of the staff of the University Press.
My friend Mr Kidston of Stirling has always generously responded to my requests for the loan of specimens from his private collection. Prof. Bayley Balfour of Edinburgh, Mr Wethered of Cheltenham and others have assisted me in a similar manner. I would also express my gratitude to Dr Hoyle of Manchester, Mr Platnauer of York, and Mr Rowntree of Scarborough for the loan of specimens.
To Dr Henry Woodward of the British Museum I am indebted for the loan of the woodblocks made use of in figs. 10, 47, 60, 66, and 101, and to Messrs Macmillan for the process-block of fig. 25.
For the photographs reproduced in figs. 15, 34, 68, 102 and 103 I owe an acknowledgment to Mr Edwin Wilson of Cambridge, and to my friend Mr C. A. Barber for the micro-photograph made use of in fig. 40.
In conclusion I wish more particularly to thank my wife, who has drawn by far the greater number of the illustrations, and has in many other ways assisted me in the preparation of this Volume.
In Volume II the Systematic treatment of Plants will be concluded, and the last chapters will be devoted to such subjects as geological floras, plants as rock-builders, fossil plants and evolution, and other general questions connected with Palaeobotany.
A. C. SEWARD.
BOTANICAL LABORATORY, CAMBRIDGE.
March, 1898.
TABLE OF CONTENTS.
PART I. GENERAL.
CHAPTER I.
=HISTORICAL SKETCH.= Pp. 1–11.
Fossil plants and the Flood. Sternberg and Brongniart. The internal structure of fossil plants. English Palaeobotanists. Difficulties of identification.
CHAPTER II. =RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY.= Pp. 12–21.
Neglect of fossils by Botanists. Fossil plants and distribution. Fossil plants and climate. Fossil plants and phylogeny.
CHAPTER III.
=GEOLOGICAL HISTORY.= Pp. 22–53.
Rock-building. Calcareous rocks. Geological sections. Inversion of strata. Table of Strata:
I. Archaean, 34–36. II. Cambrian, 36–37. III. Ordovician, 37–38. IV. Silurian, 38. V. Devonian, 39. VI. Carboniferous, 39–45. VII. Permian, 45–47. VIII. Trias., 47–48. IX. Jurassic, 48–49. X. Cretaceous, 50–51. XI. Tertiary, 51–53. Geological Evolution.
CHAPTER IV. =THE PRESERVATION OF PLANTS AS FOSSILS.= Pp. 54–92.
Old surface-soils. Fossil wood. Conditions of fossilisation. Drifting of trees. Meaning of the term ‘Fossil.’ Incrustations. Casts of trees. Fossil casts. Plants and coal. Fossils in half-relief. Petrified trees. Petrified wood. Preservation of tissues. Coal-balls. Fossil nuclei. Fossil plants in volcanic ash. Conditions of preservation.
CHAPTER V.
=DIFFICULTIES AND SOURCES OF ERROR IN THE
DETERMINATION OF FOSSIL PLANTS.= Pp. 93–109.
External resemblance. Venation characters. Decorticated stems. Imperfect casts. Mineral deposits simulating plants. Traces of wood-borers in petrified tissue. Photography and illustration.
CHAPTER VI.
=NOMENCLATURE.= Pp. 110–115.
Rules for nomenclature. The rule of priority. Terminology and convenience.
PART II. SYSTEMATIC.
CHAPTER VII.
=THALLOPHYTA.= Pp. 116–228.
=PAGE=
I. =PERIDINIALES= 117–118
II. =COCCOSPHERES AND RHABDOSPHERES= 118–121
III. =SCHIZOPHYTA= 121–138 A. SCHIZOPHYCEAE (CYANOPHYCEAE) 122–132 Girvanella 124–126. Borings in shells 127–129. Zonatrichites 129–130.
B. SCHIZOMYCETES (BACTERIA) 132–138 Bacillus Permicus 135–136. B. Tieghemi and Micrococcus Guignardi 136. Fossil Bacteria 137–138.
IV. =ALGAE= 138–205 Scarcity of fossil algae. Fossils simulating Algae. Recognition of fossil algae. Algites &c.
A. DIATOMACEAE 150–156 Recent Diatoms. Fossil Diatoms. Bactryllium &c.
B. CHLOROPHYCEAE 156–178 a. SIPHONEAE 157–177 α. =Caulerpaceae= 157–159 β. =Codiaceae= 159–164 Codium 159–160. Sphaerocodium 160. Penicillus 161. Ovulites 161–164. Halimeda 164. γ. =Dasycladaceae= 164–177 Acetabularia 165–166. Acicularia 166–169. Cymopolia 169–171. Vermiporella 172–173. Sycidium 173. Diplopora 174–175. Gyroporella 175. Dactylopora, Palaeozoic and Mesozoic Siphoneae 175–177. b. CONFERVOIDEAE 177–178
C.INCERTAE SEDIS 178–183 Boghead ‘Coal.’ Reinschia 180–181. Pila 181–182.
D. RHODOPHYCEAE 183–190 CORALLINACEAE 183–190 Lithothamnion 185–189. Solenopora 189–190.
E. PHAEOPHYCEAE 191–202 Nematophycus 192–202 Pachytheca 202–204 Algites 204–205
V. =MYXOMYCETES (MYCETOZOA)= 205–206 Myxomycetes Mangini 206.
VI. =FUNGI= 207–222 ASCOMYCETES. BASIDIOMYCETES. Pathology of fossil tissues. Oochytrium Lepidodendri 216–217. Peronosporites antiquarius 217–220. Cladosporites bipartitus 220. Haplographites cateniger 220. Zygosporites 220–221. Polyporus vaporarius 221.
VII. =CHAROPHYTA= 222–228 CHAREAE 223–228 Chara 225–228. C. Bleicheri 226. C. Knowltoni 226–227. C. Wrighti 227.
CHAPTER VIII.
=BRYOPHYTA.= Pp. 229–241.
I. =HEPATICAE= 230–236 Marchantites 233–235. M. Sezannensis 234–235.
II. =MUSCI= 236–241 Muscites 238–241. M. polytrichaceus 239–240. Palaeozoic Mosses. Muscites ferrugineus 241.
CHAPTER IX. =PTERIDOPHYTA (VASCULAR CRYPTOGRAMS).= Pp. 242–294.
I. =EQUISETALES (RECENT)= 244–254 EQUISETACEAE 244–254 Equisetum 246–254.
II. =FOSSIL EQUISETALES= 254–294 A. EQUISETITES 257–281 Equisetites Hemingwayi 263–264. E. spatulatus 264–266. E. zeaeformis 266. E. arenaceus 268–269. E. columnaris 269–270. E. Beani 270–275. E. lateralis 275–279. E. Burchardti 279–280. B. PHYLLOTHECA 281–291 Phyllotheca deliquescens 283–284. P. Brongniarti 286–287. P. indica and P. australis 287–289. C. SCHIZONEURA 291–294 S. gondwanensis 292–293.
CHAPTER X.
=EQUISETALES (continued).= Pp. 295–388.
D. CALAMITES 295–383
I. =Historical sketch= 295–302
II. =Description of the anatomy of Calamites= 302–364 a. Stems 304–329 Arthropitys, Arthrodendron, and Calamodendron. b. Leaves 329–342 α. Calamocladus (Asterophyllites) 332–336. C. equisetiformis 335–336. β. Annularia 336–342. A. stellata 338–340. A. sphenophylloides 341–342. c. Roots 342–349 d. Cones 349–365 Calamostachys Binneyana 351–355. C. Casheana 355–357. Palaeostachya vera 358–360. Calamostachys, Palaeostachya and Macrostachya 361–364.
III. =Pith-casts of Calamites= 365–380 Calamitina 367–374. Calamites (Calamitina) Göpperti 372–374. Stylocalamites 374–376. C. (Stylocalamites) Suckowi 374–376. Eucalamites 376–379. C. (Eucalamites) cruciatus 378–379.
IV. =Conclusion= 381–383
E. ARCHAEOCALAMITES 383–388 A. scrobiculatus 386–387.
CHAPTER XI.
SPHENOPHYLLALES. Pp. 389–414.
I. =SPHENOPHYLLUM= 389–414 A. =The anatomy of Sphenophyllum= 392–406 a. Stems 392–398 Sphenophyllum insigne and S. plurifoliatum 397–398. b. Roots 399 c. Leaves 399 d. Cones 401–406 Sphenophyllostachys Dawsoni 402–405. S. Römeri 405–406.
B. =Types of vegetative Branches of Sphenophyllum= 407–412 Sphenophyllum emarginatum 407–408. S. trichomatosum 408–409. S. Thoni 410–411. S. speciosum 411–412.
C. =Affinities, Range and Habit of Sphenophyllum= 412–414
LIST OF ILLUSTRATIONS.
FRONTISPIECE. TREE STUMPS IN A CARBONIFEROUS FOREST. Drawn from a photograph. (M. Seward.) PAGE 57.
FIG. PAGE 1. Lepidodendron. (M. S.) 10 2. Geological section 29 3. Table of strata 32, 33 4. Geological section (coal seam) 44 5. Neuropteris Scheuchzeri Hoffm. (M. S.) 45 6. Submerged Forest at Leasowe. (M. S.) 59 7. Ammonite on coniferous wood. (M. S.) 61 8. Coniferous wood in flint. (M. S.) 62 9. Bored fossil wood. (M. S.) 62 10. Section of an old pool filled up with a mass of Chara. (From block lent by Dr Woodward) 69 11. Equisetites columnaris Brongn. (M. S.) 72 12. Stigmaria ficoides Brongn. (M. S.) 73 13. Cordaites etc. in coal. (M. S.) 76 14. Crystallisation in petrified tissues 81 15. Lepidodendron. (From a photograph by Mr Edwin Wilson of a specimen lent by Mr Kidston) 82 16. Cast of a fossil cell. (M. S.) 84 17. Calcareous nodule from the Coal-Measures 85 18. Lepidodendron from Arran. (M. S.) 89 19. Trigonocarpon seeds in a block of sandstone. (M. S.) 91 20. Restio, Equisetum, Casuarina and Ephedra. (M. S.) 95 21. Polygonum equisetiforme Sibth. and Sm. (M. S.) 96 22. Kaulfussia æsculifolia Blume. (M. S.) 97 23. A branched Lepidodendroid stem (Knorria mirabilis Ren. and Zeill.). (M. S.) 102 24. Partially disorganised petrified tissue 107 25. Coccospheres and Rhabdospheres. (Lent by Messrs Macmillan) 119 26. Girvanella problematica Eth. and Nich. (M. S.) 124 27. Fish-scale and shell perforated by a boring organism. (M. S.) 128 28. Bacillus Tieghemi Ren. and Micrococcus Guignardi Ren. (M. S.) 135 29. Laminaria sp. 140 30. Rill-mark; trail of a seaweed; tracks of a Polychaet. (M. S.) 143 31. Chondrites verisimilis Salt. (M. S.) 146 32. Lithothamnion mamillosum Gümb.; Sycidium melo Sandb.; Bactryllium deplanatum Heer; Calcareous pebble from a lake in Michigan. (M. S.) 155 33. Cymopolia barbata (L.); Acicularia Andrussowi Solms; Acicularia sp.; A. Schencki (Möb.); A. Mediterranea Lamx.; Ovulites margaritula Lamx.; Penicillus pyramidalis (Lamx.) (M. S.) 162 34. Acetabularia mediterranea Lamx. (Photograph by Mr Edwin Wilson) 165 35. Diplopora; Gyroporella; Penicillus; Ovulites margaritula Lam.; Confervites chantransioides (Born.) 174 36. Torbanite; Pila bibractensis and Reinschia australis 180 37. Lithothamnion sp.; L. suganum Roth.; Sphaerocodium Bornemanni Roth. 186 38. Solenopora compacta (Billings). (M. S.) 189 39. Nematophycus Logani (Daws.) 196 40. Nematophycus Storriei Barb. (Photograph by Mr C. A. Barber) 199 41. Cells of Cycadeoidea gigantea Sew., Osmundites Dowkeri Carr and Memecylon with vacuolated contents; Peronosporites antiquarius Smith; Zygosporites 214 42. Tracheids of coniferous wood attacked by Trametes radiciperda Hart and Agaricus melleus Vahl. 215 43. Oochytrium Lepidodendri Ren.; Polyporus vaporarius Fr. var. succinea; Cladosporites bipartitus Fel.; Haplographites cateniger Fel. (M. S.) 217 44. Cells of fossil plants with fungal hyphae 219 45. Chara Knowltoni Sew.; Chara foetida A. Br. (A and B, Mr Highley; C–E, M. S.) 224 46. Chara Bleicheri Sap.; Chara? sp.; C. Wrighti Forbes. (M. S.) 226 47. Chara Knowltoni Sew. (From block lent by Dr Woodward) 227 48. Tristichia hypnoides Spreng.; Podocarpus cupressina Br. and Ben.; Selaginella Oregana Eat. (M. S.) 231 49. Marchantites erectus (Leck.) (M. S.) 233 50. Marchantites Sezannensis Sap. (M. S.) 235 51. Muscites polytrichaceus Ren. and Zeill. (M. S.) 239 52. Equisetum maximum Lam.; E. arvense L. 246 53. Equisetum palustre L. (M. S.) 247 54. Plan of the vascular bundles in an Equisetum stem; E. arvense L. 250 55. Equisetum variegatum Schl.; E. maximum Lam. 252 56. Calamitean leaf-sheath. (M. S.) 260 57. Equisetites Hemingwayi Kidst. (Mr Highley) 262 58. Equisetites spatulatus Zeill.; E. zeaeformis (Schloth.); Equisetites lateralis Phill.; Equisetites columnaris Brongn.; Equisetum trachyodon A. Br. (M. S.) 265 59. Equisetites platyodon Brongn. (M. S.) 267 60. Equisetites Beani (Bunb.). (From a block lent by Dr Woodward) 271 61. Equisetites Beani (Bunb.). (M. S.) 272 62. E. Beani (Bunb.). (M. S.) 274 63. E. lateralis Phill. (M. S.) 275 64. E. lateralis Phill. (M. S.) 278 65. E. Burchardti Dunk. (M. S.) 279 66. E. Yokoyamae Sew. (From a block lent by Dr Woodward) 280 67. Phyllotheca? sp. (From a photograph by Mr Edwin Wilson) 285 68. Phyllotheca Brongniarti Zigno; P. indica Bunb.; Calamocladus frondosus Grand’Eury. (M. S.) 287 69. Schizoneura gondwanensis Feist. (M. S.) 293 70. Transverse section of a Calamite stem. (M. S.) 299 71. Transverse section of a young Calamite stem 305 72. Longitudinal and transverse sections of Calamites 308 73. Transverse section of a Calamite stem 310 74. Transverse section of Calamites (Arthropitys) sp. 312 75. Longitudinal section (tangential) of Calamites (Arthropitys) sp. 313 76. Longitudinal section (tangential) of Calamites (Arthropitys) sp. 314 77. Portion of a Calamite stem; partially restored. (M. S.) 316 78.╮ Transverse and longitudinal (radial) sections of a thick 318 79.╯ Calamite stem. (Mr Highley) 319 80. Transverse section of a Calamite showing callus wood 320 81. Longitudinal section of a young Calamite 321 82. Pith-casts of Calamites (Stylocalamites) sp. (M. S.) 323 83. Calamites (Arthrodendron) sp. Transverse and longitudinal sections 327 84. Transverse section of Calamites (Calamodendron) intermedius Ren. 328 85. Leaves of a Calamite. (M. S.) 330 86. Transverse section of a Calamite leaf 331 87. Calamocladus equisetiformis (Schloth.) (Miss G. M. Woodward) 334 88. Annularia stellata (Schloth.) (M. S.) 339 89. Annularia sphenophylloides Zenk. (M. S.) 340 90. Pith-cast of a Calamite, with roots. (M. S.) 343 91. Transverse sections of Calamite roots 345 92. Root given off from a Calamite stem 347 93. Calamostachys sp. (M. S.) 350 94. C. Binneyana (Carr.). (Mr Highley) 352 95. C. Binneyana (Carr.) 354 96. C. Casheana Will. 356 97. Palaeostachya pedunculata Will. (M. S.) 357 98. P. vera sp. nov. 359 99. Calamites (Calamitina) Göpp. (Ett.) (M. S.) 368 100. Calamites (Calamitina) approximatus Brongn. From a photograph by Mr Kidston 370 101. Calamites (Calamitina) sp. (From a block lent by Dr Woodward) 373 102. Calamites (Eucalamites) cruciatus Sternb. (From a photograph by Mr Edwin Wilson) 377 103. Archaeocalamites scrobiculatus (Schloth.). (From a photograph by Mr Edwin Wilson) 385 104. Diagrammatic longitudinal section of Sphenophyllum 393 105. Transverse and longitudinal sections of Sphenophyllum insigne (Will.) and S. plurifoliatum Will. and Scott 394 106. Sphenophyllum plurifoliatum Will. and Scott. (From a photograph by Mr Highley) 398 107. Sphenophyllum strobilus, stem and root 400 108. Diagrammatic longitudinal section of a Sphenophyllum strobilus. (M. S.) 402 109. Sphenophyllum emarginatum (Brongn.) (M. S.) 407 110. Sphenophyllum Thoni Mahr.; S. trichomatosum Stur. (M. S.) 410 111. Sphenophyllum speciosum (Royle). (M. S.) 411
=Note.= The references in the footnotes require a word of explanation. The titles of the works referred to will be found in the Bibliography at the end of the volume. In this list the authors’ names are arranged alphabetically and the papers of each author are in chronological order. The numbers in brackets after the author’s name in the footnotes, and before his name in the bibliographical list, refer to the year of publication. Except in cases where the works were published prior to 1800, the first two figures are omitted: thus Ward (84) refers to a paper published by L. F. Ward in 1884. This system was suggested by Dr H. H. Field in the Biologisches Centralblatt, vol. XIII. 1893, p. 753. (Ueber die Art der Abfassung naturwissenschaftlicher Litteraturverzeichnisse.)
=PART I. GENERAL.=
CHAPTER I.
HISTORICAL SKETCH.
“But particular care ought to be had not to consult or take relations from any but those who appear to have been both long conversant in these affairs, and likewise persons of Sobriety, Faithfulness and Discretion, to avoid the being misled and imposed upon either by falsehood, or the ignorance, credulity, and fancifulness, that some of these people are but too obnoxious unto.” JOHN WOODWARD, 1728.
The scientific study of fossil plants dates from a comparatively recent period, and palaeobotany has only attained a real importance in the eyes of botanists and geologists during the last few decades of the present century. It would be out of place, in a short treatise like the present, to attempt a detailed historical sketch, or to give an adequate account of the gradual rise and development of this modern science. An excellent Sketch of Palaeobotany has recently been drawn up by Prof. Lester Ward[1], of the United States Geological Survey, and an earlier historical retrospect may be found in the introduction to an important work by an eminent German palaeobotanist, the late Prof. Göppert[2]. In the well-known work by Parkinson on _The Organic Remains of a Former World_[3] there is much interesting information as to the early history of our knowledge of fossil plants, as well as a good exposition of the views held at the beginning of this century.
[Sidenote: FOSSIL PLANTS AND THE FLOOD.]
As a means of bringing into relief the modern development of the science of fossil plants, we may briefly pass in review some of the earlier writers, who have concerned themselves in a greater or less degree with a descriptive or speculative treatment of the records of a past vegetation. In the early part of the present century, and still more in the eighteenth century, the occurrence of fossil plants and animals in the earth’s crust formed the subject of animated, not to say acrimonious, discussion. The result was that many striking and ingenious theories were formulated as to the exact manner of formation of fossil remains, and the part played by the waters of the deluge in depositing fossiliferous strata. The earlier views on fossil vegetables are naturally bound up with the gradual evolution of geological science. It is from Italy that we seem to have the first glimmering of scientific views; but we are led to forget this early development of more than three hundred years ago, when we turn to the writings of English and other authors of the eighteenth century. “Under these white banks by the roadside,” as a writer on Verona has expressed it, “was born, like a poor Italian gipsy, the modern science of geology.” Early in the sixteenth century the genius of Leonardo da Vinci[4] compelled him to adopt a reasonable explanation of the occurrence of fossil shells in rocks far above the present sea-level. Another Italian writer, Fracastaro, whose attention was directed to this matter by the discovery of numerous shells brought to light by excavations at Verona, expressed his belief in the organic nature of the remains, and went so far as to call in question the Mosaic deluge as a satisfactory explanation of the deposition of fossil-bearing strata.
The partial recognition by some observers of the true nature of fossils marks the starting point of more rational views. The admission that fossils were not mere sports of nature, or the result of some wonderful ‘vis lapidifica,’ was naturally followed by numerous speculations as to the manner in which the remains of animals and plants came to be embedded in rocks above the sea-level. For a long time, the ‘universal flood’ was held responsible by nearly all writers for the existence of fossils in ancient sediments. Dr John Woodward, in his Essay toward a Natural History of the Earth, propounded the somewhat revolutionary theory, that “the whole terrestrial globe was taken all to pieces and dissolved at the Deluge, the particles of stone, marble, and all solid fossils dissevered, taken up into the water, and there sustained together with sea-shells and other animal and vegetable bodies: and that the present earth consists, and was formed out of that promiscuous mass of sand, earth, shells, and the rest falling down again, and subsiding from the water[5].” In common with other writers, he endeavoured to fix the exact date of the flood by means of fossil plants. Speaking of some hazel-nuts, which were found in a Cheshire moss pit, he draws attention to their unripened condition, and adds: “The deluge came forth at the end of May, when nuts are not ripe.” As additional evidence, he cites the occurrence of “Pine cones in their vernal state,” and of some Coal-Measure fossils which he compares with Virginian Maize, “tender, young, vernal, and not ripened[6].” Woodward (1665–1728) was Professor of Physic in Gresham College; he bequeathed his geological collections to the University of Cambridge, and founded the Chair which bears his name.
Another writer, Mendes da Costa, in a paper in the Philosophical Transactions for 1758, speaks of the impressions of “ferns and reed-like plants” in the coal-beds, and describes some fossils (Sigillaria and Stigmaria) as probably unknown forms of plant life[7].
Here we have the suggestion that in former ages there were plants which differed from those of the present age. Discussing the nature of some cones (Lepidostrobi) from the ironstone of Coalbrookdale in Shropshire, he concludes: “I firmly believe these bodies to be of vegetable origin, buried in the strata of the Earth at the time of the universal deluge recorded by Moses.” Scheuchzer of Zurich, the author of one of the earliest works on fossil plants and a “great apostle of the Flood Theory,” figures and describes a specimen as an ear of corn, and refers to its size and general appearance as pointing to the month of May as the time of the deluge[8]. Another English writer, Dr Parsons, in giving an account of the well-known ‘fossil fruits and other bodies found in the island of Sheppey,’ is disposed to dissent from Woodward’s views as to the time of the flood. He suggests that the fact of the Sheppey fruits being found in a perfectly ripe condition, points to the autumn as the more probable time for the occurrence of the deluge[9].
In looking through the works of the older writers, and occasionally in the pages of latter-day contributors, we frequently find curiously shaped stones, mineral markings on rock surfaces, or certain fossil animals, described as fossil plants. In Plot’s Natural History of Oxfordshire, published in 1705, a peculiarly shaped stone, probably a flint, is spoken of as one of the ‘Fungi lethales non esculenti[10]’; and again a piece of coral[11] is compared with a ‘Bryony root broken off transversely.’ On the other hand, that we may not undervalue the painstaking and laborious efforts of those who helped to lay the foundations of modern science, we may note that such authors as Scheuchzer and Woodward were not misled by the moss-like or dendritic markings of oxide of manganese on the surface of rocks, which are not infrequently seen to-day in the cabinets of amateurs as specimens of fossil plants.
The oldest figures of fossil plants from English rocks which are drawn with any degree of accuracy are those of Coal-Measure ferns and other plants in an important work by Edward Lhwyd published at Oxford in 1760[12].
Passing beyond these prescientific speculations, brief reference may be made to some of the more eminent pioneers of palaeobotany. The Englishman Artis[13] deserves mention for the quality rather than the quantity of his contributions to Palaeozoic botany; and among American authors Steinhauer’s[14] name must hold a prominent place in the list of those who helped to found this branch of palaeontology. Among German writers, Schlotheim stands out prominently as one who first published a work on fossil plants which still remains an important book of reference. Writing in 1804, he draws attention to the neglect of fossils from a scientific standpoint; they are simply looked upon, he says, as “unimpeachable documents of the flood[15].” His book contains excellent figures of many Coal-Measure plants, and we find in its pages occasional comparisons of fossil species with recent plants of tropical latitudes. Among the earlier authors whose writings soon become familiar to the student of fossil plants, reference must be made to Graf Sternberg, who was born three years before Schlotheim, but whose work came out some years later than that of the latter. His great contribution to Fossil Botany entitled Versuch einer geognostisch-botanischen Darstellung der Flora der Vorwelt, was published in several parts between the years 1820 and 1838; it was drawn up with the help of the botanist Presl, and included a valuable contribution by Corda[16]. In addition to descriptions and numerous figures of plants from several geological horizons, this important work includes discussions on the formation of coal, with observations on the climates of past ages.
[Sidenote: STERNBERG AND BRONGNIART.]
Sternberg endeavoured to apply to fossil plants the same methods of treatment as those made use of in the case of recent species. About the same time as Sternberg’s earlier parts were published, Adolphe Brongniart[17] of Paris began to enrich palaeobotanical science by those splendid researches which have won for him the title of the “Father of palaeobotany.” In Brongniart’s Prodrome, and Histoire des végétaux fossiles, and later in his Tableau des genres de végétaux fossiles, we have not merely careful descriptions and a systematic arrangement of the known species of fossil plants, but a masterly scientific treatise on palaeobotany in its various aspects, which has to a large extent formed the model for the best subsequent works on similar lines. From the same author, at a later date, there is at least one contribution to fossil plant literature which must receive a passing notice even in this short sketch. In 1839 he published an exhaustive account of the minute structure of one of the well-known Palaeozoic genera, Sigillaria; this is not only one of the best of the earliest monographs on the histology of fossil species, but it is one of the few existing accounts of the internal structure of this common type[18]. The fragment of a Sigillarian stem which formed the subject of Brongniart’s memoir is in the Natural History Museum in the Jardin des Plantes, Paris. It affords a striking example of the perfection of preservation as well as of the great beauty of the silicified specimens from Autun, in Central France. Brongniart was not only a remarkably gifted investigator, whose labours extend over a period connecting the older and more crude methods of descriptive treatment with the modern development of microscopic analysis, but he possessed the power of inspiring a younger generation with a determination to keep up the high standard of the palaeobotanical achievements of the French School. In some cases, indeed, his disciples have allowed a natural reverence for the Master to warp their scientific judgement, where our more complete knowledge has naturally led to the correction of some of Brongniart’s conclusions. Without attempting to follow the history of the science to more recent times, the names of Heer, Lesquereux, Zigno, Massalongo, Saporta and Ettingshausen should be included among those who rendered signal service to the science of fossil plants. The two Swiss writers, Heer[19] and Lesquereux[20], contributed numerous books and papers on palaeobotanical subjects, the former being especially well known in connection with the fossil floras of Switzerland and of Arctic lands, and the latter for his valuable writings on the fossil plants of his adopted country, North America. Zigno[21] and Massalongo[22] performed like services for Italy, and the Marquis of Saporta’s name will always hold an honourable and prominent position in the list of the pioneers of scientific palaeobotany; his work on the Tertiary and Mesozoic floras of France being specially noteworthy among the able investigations which we owe to his ability and enthusiasm[23]. In Baron Ettingshausen[24] we have another representative of those students of ancient vegetation who have done so much towards establishing the science of fossil plants on a philosophical basis.
As in other fields of Natural Science, so also in a marked degree in fossil botany, a new stimulus was given to scientific inquiry by the application of the microscope to palaeobotanical investigation. In 1828 Sprengel published a work entitled _Commentatio de Psarolithis, ligni fossilis genere_[25]; in which he dealt in some detail with the well-known silicified fern-stems of Palaeozoic age, from Saxony, basing his descriptions on the characteristics of anatomical structure revealed by microscopic examination.
[Sidenote: THE INTERNAL STRUCTURE OF FOSSIL PLANTS.]
In 1833 Henry Witham of Lartington brought out a work on _The Internal Structure of Fossil Vegetables_[26]; this book, following the much smaller and less important work by Sprengel, at once established palaeobotany on a firmer scientific basis, and formed the starting point for those more accurate methods of research, which have yielded such astonishing results in the hands of modern workers. In the introduction Witham writes, “My principal object in presenting this work to the public, is to impress upon geologists the advantage of attending more particularly to the intimate organization of fossil plants; and should I succeed in directing their efforts towards the elucidation of this obscure subject, I shall feel a degree of satisfaction which will amply repay my labour[27].”
On another page he writes as follows,—“From investigations made by the most active and experienced botanical geologists, we find reason to conclude that the first appearance of an extensive vegetation occurred in the Carboniferous series; and from a recent examination of the mountain-limestone groups and coal-fields of Scotland, and the north of England, we learn that these early vegetable productions, so far from being simple in their structure, as had been supposed, are as complicated as the phanerogamic plants of the present day. This discovery necessarily tends to destroy the once favourite idea, that, from the oldest to the most recent strata, there has been a progressive development of vegetable and animal forms, from the simplest to the most complex[28].” Since Witham’s day we have learnt much as to the morphology of Palaeozoic plants, and can well understand the opinions to which he thus gives expression.
It would be difficult to overrate the immense importance of this publication from the point of view of modern palaeobotany.
The art of making transparent sections of the tissues of fossil plants seems to have been first employed by Sanderson, a lapidary, and it was afterwards considerably improved by Nicol[29]. This most important advance in methods of examination gave a new impetus to the subject, but it is somewhat remarkable that the possibilities of the microscopical investigation of fossil plants have been but very imperfectly realised by botanical workers until quite recent years. As regards such a flora as that of the Coal-Measures, we can endorse the opinion expressed at the beginning of the century in reference to the study of recent mosses—“Ohne das Göttergeschenk des zusammengesetzten Mikroskops ist auf diesem Felde durchaus keine Ernte[30].” A useful summary of the history of the study of internal structure is given by Knowlton in a memoir published in 1889[31]. Not long after Witham’s book was issued there appeared a work of exceptional merit by Corda[32], in which numerous Palaeozoic plants are figured and fully described, mainly from the standpoint of internal structure. This author lays special stress on the importance of studying the microscopical structure of fossil plants.
[Sidenote: ENGLISH PALAEOBOTANISTS.]
Without pausing to enumerate the contributions of such well-known continental authors as Göppert, Cotta, Schimper, Stenzel, Schenk and a host of others, we may glance for a moment at the services rendered by English investigators to the study of palaeobotanical histology. Unfortunately we cannot always extend our examination of fossil plants beyond the characters of external form and surface markings; but in a few districts there are preserved remnants of ancient floras in which fragments of stems, roots, leaves and other structures have been petrified in such a manner as to retain with wonderful completeness the minute structure of their internal tissues. During the deposition of the coal seams in parts of Yorkshire and Lancashire the conditions of fossilisation were exceptionally favourable, and thus English investigators have been fortunately placed for conducting researches on the minute anatomy of the Coal-Measure plants. The late Mr Binney of Manchester did excellent service by his work on the internal structure of some of the trees of the Coal Period forests. In his introductory remarks to a monograph on the genus Calamites, after speaking of the desirability of describing our English specimens, he goes on to say, “When this is done, we are likely to possess a literature on our Carboniferous fossils worthy of the first coal-producing country[33].” The continuation and extension of Binney’s work in the hands of Carruthers, Williamson, and others, whose botanical qualifications enabled them to produce work of greater scientific value, has gone far towards the fulfilment of Binney’s prophecy.
[Sidenote: DIFFICULTIES OF IDENTIFICATION.]
In dealing with the structure of Palaeozoic plants, we shall be under constant obligation to the splendid series of memoirs from the pen of Prof. Williamson[34]. As the writer of a sympathetic obituary notice has well said: “In his fifty-fifth year he began the great series of memoirs which mark the culminating point of his scientific activity, and which will assure to him, for all time, in conjunction with Brongniart, the honourable title of a founder of modern Palaeobotany[35].” If we look back through a few decades, and peruse the pages of Lindley and Hutton’s classic work[36] on the Fossil flora of Great Britain, a book which is indispensable to fossil botanists, and read the description of such a genus as Sigillaria or Stigmaria; or if we extend our retrospect to an earlier period and read Woodward’s description of an unusually good specimen of a Lepidodendron, and finally take stock of our present knowledge of such plants, we realise what enormous progress has been made in palaeobotanical studies. Lindley and Hutton, in the preface to the first volume of the Flora, claim to have demonstrated that both Sigillaria and Stigmaria were plants with “the highest degree of organization, such as Cactaeae, or Euphorbiaceae, or even Asclepiadeae”; Woodward describes his Lepidodendron (Fig. 1) as “an ironstone, black and flat, and wrought over one surface very finely, with a strange cancellated work[37].” Thanks largely to the work of Binney, Carruthers, Hooker, Williamson, and to the labours of continental botanists, we are at present almost as familiar with Lepidodendron and several other Coal-Measure genera as with the structure of a recent forest tree. While emphasizing the value of the microscopic methods of investigation, we are not disposed to take such a hopeless view of the possibilities of the determination of fossil forms, in which no internal structure is preserved, as some writers have expressed. The preservation of minute structure is to be greatly desired from the point of view of the modern palaeobotanist, but he must recognise the necessity of making such use as he can of the numberless examples of plants of all ages, which occur only in the form of structureless casts or impressions.
FIG. 1. Four leaf-cushions of a Lepidodendron. Drawn from a specimen in the Woodward Collection, Cambridge. (Nat. size.)
In looking through the writings of the earlier authors we cannot help noticing their anxiety to match all fossil plants with living species; but by degrees it was discovered that fossils are frequently the fragmentary samples of extinct types, which can be studied only under very unfavourable conditions. In the absence of those characters on which the student of living plants relies as guides to classification, it is usually impossible to arrive at any trustworthy conclusions as to precise botanical affinity. Brongniart and other authors recognised this fact, and instituted several convenient generic terms of a purely artificial and provisional nature, which are still in general use. The dangers and risks of error which necessarily attend our attempts to determine small and imperfect fragments of extinct species of plants, will be briefly touched on in another place.
CHAPTER II.
RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY.
“La recherche du plan de la création, voilà le but vers lequel nos efforts peuvent tendre aujourd’hui.” GAUDRY, 1883.
Since the greater refinements and thoroughness of scientific methods and the enormous and ever-increasing mass of literature have inevitably led to extreme specialisation, it is more than ever important to look beyond the immediate limits of one’s own subject, and to note its points of contact with other lines of research. A palaeobotanist is primarily concerned with the determination and description of fossil plants, but he must at the same time constantly keep in view the bearing of his work on wider questions of botanical or geological importance. From the nature of the case, we have in due measure to adapt the methods of work to the particular conditions before us. It is impossible to follow in the case of all fossil species precisely the same treatment as with the more complete and perfect recent plants; but it is of the utmost importance for a student of palaeobotany, by adhering to the methods of recent botany, to preserve as far as he is able the continuity of the past and present floras. Palaeontological work has often been undertaken by men who are pure geologists, and whose knowledge of zoology or botany is of the most superficial character, with the result that biologists have not been able to avail themselves, to any considerable extent, of the records of extinct forms of life. They find the literature is often characterised by a special palaeontological phraseology, and by particular methods of treatment, which are unknown to the student of living plants and animals. From this and other causes a purely artificial division has been made between the science of the organic world of to-day and that of the past.
[Sidenote: NEGLECT OF FOSSILS BY BOTANISTS.]
Fossils are naturally regarded by a stratigraphical geologist as records which enable him to determine the relative age of fossil-bearing rocks. For such a purpose it is superfluous to inquire into the questions of biological interest which centre round the relics of ancient floras. Primarily concerned, therefore, with fixing the age of strata, it is easy to understand how geologists have been content with a special kind of palaeontology which is out of touch with the methods of systematic zoology or botany. On the other hand, the botanist whose observations and researches have not extended beyond the limits of existing plants, sees in the vast majority of fossil forms merely imperfect specimens, which it is impossible to determine with any degree of scientific accuracy. He prefers to wait for perfect material; or in other words, he decides that fossils must be regarded as outside the range of taxonomic botany. It would seem, then, that the unsatisfactory treatment or comparative neglect of fossil plants, has been in a large measure due to the narrowness of view which too often characterises palaeobotanical literature. This has at once repelled those who have made a slight effort to recognise the subject, and has resulted in a one-sided and, from a biological standpoint, unscientific treatment of this branch of science. It must be admitted that palaeobotanists have frequently brought the subject into disrepute by their over-anxiety to institute specific names for fragments which it is quite impossible to identify. This over-eagerness to determine imperfect specimens, and the practice of drawing conclusions as to botanical affinity without any trustworthy evidence, have naturally given rise to considerable scepticism as to the value of palaeobotanical records. Another point, which will be dealt with at greater length in a later chapter, is that geologists have usually shown a distinct prejudice against fossil plants as indices of geological age; this again, is no doubt to a large extent the result of imperfect and inaccurate methods of description, and of the neglect of and consequent imperfect acquaintance with fossil plants as compared with fossil animals.
The student of fossil plants should endeavour to keep before him the fact that the chief object of his work is to deal with the available material in the most natural and scientific manner; and by adopting the methods of modern botany, he should always aim to follow such lines as may best preserve the continuity of past and present types of plants. Descriptions of floras of past ages and lists of fossil species, should be so compiled that they may serve the same purpose to a stratigraphical geologist, who is practically a geographer of former periods of the Earth’s history, as the accounts of existing floras to students of present day physiography. The effect of carrying out researches on some such lines as these, should be to render available to both botanists and geologists the results of the specialist’s work.
In some cases, palaeobotanical investigations may be of the utmost service to botanical science, and of little or no value to geology. The discovery of a completely preserved gametophyte of Lepidodendron or Calamites, or of a petrified Moss plant in Palaeozoic rocks would appeal to most botanists as a matter of primary importance, but for the stratigraphical geologist such discoveries would possess but little value. On the other hand the discovery of some characteristic species of Coal-Measure plants from a deep boring through Mesozoic or Tertiary strata might be a matter of special geological importance, but to the botanist it would be of no scientific value. In very many instances, however, if the palaeobotanist follows such lines as have been briefly suggested, the results of his labours should be at once useful and readily accessible to botanists and geologists. As Humboldt has said in speaking of Palaeontology, “the analytical study of primitive animal and vegetable life has taken a double direction; the one is purely morphological, and embraces especially the natural history and physiology of organisms, filling up the chasms in the series of still living species by the fossil structures of the primitive world. The second is more specially geognostic, considering fossil remains in their relations to the superposition and relative age of the sedimentary formations[38].”
[Sidenote: FOSSIL PLANTS AND DISTRIBUTION.]